Functional density, i.e., number of interconnected devices per chip, of semiconductor integrated circuits (ICs) has increased over the years. This increase in functional density has been achieved by reducing the size of individual devices on the chip. Semiconductor manufacturing techniques such as photolithography needed to continue this decreasing trend in size of devices is met by decreasing the wavelength of light used in photolithography.
For example, the wavelength of radiation used for photolithography has decreased from ultraviolet to deep ultraviolet (DUV) and, more recently to extreme ultraviolet (EUV). Further decreases in component size require further improvements in resolution of photolithography which are achievable using extreme ultraviolet lithography (EUVL). EUVL employs radiation having a wavelength of about 1-100 nm.
Because radiation in the EUV range is ionizing radiation, EUVL is generally performed in low-pressure or vacuum-like conditions. In such conditions, suction-based mask holders generally used for DUV photolithography do not work. An electrostatic reticle holder is, therefore, used for securing the mask or reticle used for EUVL.